1. Field of the Invention
The present invention relates to a photovoltaic electrochromic device and a method of manufacturing the same.
2. Description of Related Art
In view of structure, typical electrochromic devices are divided into a solid type and a liquid type. The structure of a solid-type electrochromic device 100 includes two glass or plastic transparent substrates 102. At least five coating/plating layers (such as a transparent conductive layer 104, an electrochromic thin film 106, a solid electrolyte 108, and an ion storage layer 110) which respectively has different function, are disposed between the two substrates 102, like a sandwich, to constitute a battery-like structure, as shown in FIG. 1. The structure of a liquid-type electrochromic device 200 is formed by two transparent conductive substrates 202. One or two sides of the anodes and the cathodes on two opposite transparent conductive substrates 202 are respectively coated/plated with a transparent conductive electrochromic layer 204, and an electrolyte solution 206 is added between the transparent conductive substrates 202, as shown in FIG. 2.
Compared to electrochromic device which has been developed for some time, the integration of photovoltaic and electrochromic technologies provides better efficiency in energy saving, for photovoltaic electrochromic device can achieve color change in electrochromic layers without additional power source. At the beginning, photovoltaic electrochromic technology is developed based on the concept of using compound films of a Prussian blue electrochromic thin film and a photosensitive layer-TiO2 for performing color change. In recent years, such a concept has been further extended to separate the photosensitive layer and the electrochromic layer to the anode and the cathode respectively for constituting a device. This kind of device can be described as having electrochromic materials inserted into dye sensitive solar cells, which has become the most widely-discussed subject in the research of photoelectrochromic technology. The electrochromic material is WO3 and the dye sensitive solar cell mainly utilizes Ruthenium Ru-dye. The structure of a photoelectrochromic device 300 is shown in FIG. 3. The photoelectrochromic device 300 is a multi-layer photoelectrochemical device that includes two transparent conductive substrates 302, a working electrode layer 304 formed of photosensitive material and disposed between the transparent conductive substrates 302, an electrolyte layer 306, and an auxiliary electrode layer 308 formed of electrochromic material.
U.S. Pat. No. 6,369,934B1 has disclosed a whole organic multi-layer photoelectrochemical device, for instance. However, to apply such a structure to practical applications, many problems need to be overcome such as the long term stability of the photosensitive layer and the possibility of developing devices having larger sizes.
U.S. Pat. No. 5,384,653 provides a variable transmittance of two glass panels separated from each other, wherein an electrochromic layer stack is disposed at the inner side of the first glass panel in conjunction with an array of photovoltaic cells deposited along an edge of the glass panel, to produce electric power necessary to change the color of the electrochromic layer stack. A battery is placed in parallel fashion to the array of photovoltaic cells to allow the user the ability to manually override the system to a desired transmittance.
U.S. Pat. No. 6,055,089 provides an electrochromic system that combines a solar cell with an electrochromic device, wherein an inorganic electrochromic glass is disposed in front of a silicon crystal solar cell module, and a layer of air is between the inorganic electrochromic glass and the silicon crystal solar module. Under sunlight irradiation, electricity generated by the solar cell is outputted to the electrochromic device via terminals of the cell so as to change the color of an electrochromic layer. The color contrast within the electrochromic system controls the incident light intensity falling on solar cell and thereby determines the output current of the solar cell.
U.S. Pat. No. 5,805,330 provides an all-organic structure, wherein both an upper layer and a lower layer are transparent conductive substrates, and an organic small molecule electrochromic material and an electrolyte solution are disposed therebetween. A solar cell module adheres to the edge of the electrochromic glass, so that when illuminated by sunlight, the current generated by the solar cell is supplied to the electrochromic device via an output terminal of the cell and the electrochromic device thereby changes color.
Moreover, U.S. Pat. No. 5,377,037 has disclosed a design of combining a solar cell with an electrochromic device to form one single device, which is basically manufactured by using a stacking method to combine monolithic silicon thin-film solar cells with an inorganic electrochromic device on a first conductive glass substrate, and then oppositely bonding the silicon thin-film solar cells with another transparent conductive glass substrate. Between the substrates, a liquid organic electrolyte solution or a solid inorganic electrolyte layer is disposed. The color contrast of the device is comparatively low.